Study On Microstructures,Mechanical Properties And Damping Capacities Of Rolled And Annealed Zk60-0.4%Y-0.18%Gd Alloy Sheets

The microstructures, mechanical properties and damping capacities of ZK60-0.4%Y-0.18%Gd were investigated in this thesis. Unidirectional and cross rolling at420℃and subsequently annealing treatment for some rolled sheets was employed to obtain four different sheets. The microstructures of the four states of the ZK60-0.4%Y-0.18%Gd alloy were analyzed by optical microscopy (OM), scanning electron microscopy (SEM/EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). The mechanical properties and damping capacities of different directions about sheets were tested on electronic tensile machine and DMA-Q800dynamic thermal analyzer, where the angle between tensile direction and rolling direction was0°(RD),22.5°,45°,67.5°and90°(TD). The textures of two annealed sheets were investigated by EBSD. The relationship between crystal orientation and anisotropic of mechanical properties and damping capacities was discussed. Experiment results showed as follows:1. Dynamic recrystallization of the rolled sheets had taken place during the rolling processes. The refined grains, tangled dislocations, considerable amount of twins and crushed second phases were observed. After annealing treatment, two sheets consisted of equiaxed grains, with disappearing of twins and tangled dislocations, integrating of part of second phases into matrix. Compared with the unidirectional annealed sheet, the cross annealed sheet showed more uniform microstructures and finer grain size.2. The cross rolling sheet displayed higher yield strength and ultimate tensile strength compared with the unidirectional rolling sheet. Meanwhile, the mechanical properties along five directions for the unidirectional rolling sheet showed obvious anisotropy, however, the cross rolling sheet exhibited isotropy. The strength of two sheets decreased after annealing. The strength of the cross annealed sheet was lower than that of the unidirectional rolling sheet. Anisotropy of mechanical properties was closely related to crystal orientation. Taking into account of crystal orientation distribution of polycrystalline magnesium alloy, the mechanical anisotropy of unidirectional annealed sheet and the mechanical isotropy of cross annealed sheet can be explained qualitatively based on the{0001}<11-20> basal slip and{10-10}<11-20> prismatic slip and the microscopic crystal plasticity theory.3. Damping flats observed in both unidirectional and cross rolling sheets were removed after annealing. The strain-independent damping and the strain-dependent damping for annealed sheets were higher than that of the rolled sheets. The obviously anisotropy of damping were investigated in the unidirectional rolling sheet as well as the unidirectional annealed sheet. However, the cross rolling sheet and annealing sheet exhibited isotropic damping capacities. The value of C1and C2was calculated by the G-L model and G-L graph. Combining the Schmid factor on the{0001}<11-20> basal slip, the damping performance along the direction of0°(RD),45°and90°(TD) for the unidirectional annealed sheet reduced gradually with decreased of the Schmid factor and the value of C1and C2, but the damping capacities along three directions for the cross annealed sheet was litter difference with the similar the Schmid factor and the value of Ci and C2.The author would like to express her gratitude to the National Key Basic Research Projects of China (973Program)-"Regulatory elements and organizational performance of low cost, high ductility and high strength magnesium alloys"(2013CB62202) for financial support, which is the second research subject of "The basic research of low cost, high ductility and high strength magnesium alloys".